Rotary screen printing machines are well known and typically include a frame, a backing means supported by the frame, and at least one, and usually a plurality, of rotary screen assemblies which are carried by the frame in close proximity with respect to the backing means. Typically, each rotary screen assembly includes an inner elongated support member, an outer hollow patterned screen supported about the inner elongated support member for rotation thereabout, and an elongated applicator, such as a conventional squeegee, which is supported on the inner elongated support member and engages the inner surface of the screen to press coloring paste or ink through the perforated pattern thereof as the fabric being printed is passed between the respective hollow screen and the backing means. In a rotary type screen printing machine, the backing means comprises a large drum and the plurality of rotary screen assemblies are supported circumferentially thereabout. In a flat bed screen printing machine, it is normal practice to provide the rotary screen assemblies in a common plane with each screen assembly being provided with a cooperating back-up roller associated therewith.
In the above-described types of machines, drive means are provided which drive the backing means (usually a large rotary drum) and the rotating screens of each assembly in response to rotation of the backing means. In order to effect such rotation, screen gear means are provided at one end of each of said rotary screen assemblies and a main gear, commonly referred to as a sun gear, is provided at one end of the backing means. The individual screen gears of the rotary screen assemblies engage the sun gear of the backing means so that upon rotation of the backing means and its sun gear, simultaneous rotation of said screen gears and said rotary screens connected thereto is effected. When the drive means is deactivated, this causes stoppage of the backing means and its associated sun gear and thus stoppage of rotation of said gear means and associated screens.
It is most important in the above-describe machines that the linear velocity of the rotatable screens be made to match the linear velocity of the backing means so that the printing will be accurately aligned on the fabric or other sheet material to be imprinted upon and the printed portion derived from one screen will be properly positioned with respect to the printed portion derived from another screen. Unfortunately, and contrary to normal expectation, it has been found that even where a direct linkage through the screen gears to the sun gear is employed, it is still not possible to accurately match the surface speeds of the screens and the backing means. Such failure is probably due to the variation in load on the screen when more or less pressure is applied to the squeegee as well as the variation in the viscosities of the inks or coloring pastes used.